One idea under discussion is Facebook paying users fractions of a coin when they view ads, interact with other content or shop on its platform--not unlike loyalty points accrued at retailers, some of the people said.

This would reward the kind of genuine interaction that Facebook, beset by bots and hate speech, has been trying to encourage. It could also blunt criticism that the company makes billions of dollars on the backs of its users, sometimes in troubling or invasive ways.

Creating a so-called stablecoin backed by government currency better positions it as a legitimate payment method rather than a speculative bet. The volatility of bitcoin and other cryptocurrencies that aren't backed by hard assets has hampered their usefulness in payments.

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Now Facebook must bend a variety of stakeholders to its vision. Most immediately are Visa and Mastercard Inc., whose networks handle the vast majority of credit and debit card payments in the U.S.

If it succeeds, the project threatens the card networks' dominance over global payments. Facebook comes armed with more than 1.5 billion daily users, many of them in developing countries where social-media sites provide the backbone of internet commerce.